The present invention relates to a surface treatment of powders. In particular, the invention relates to a surface treatment of powders to be used in additive manufacturing processes.
Additive manufacturing is an established but growing technology. In its broadest definition, additive manufacturing is any layerwise construction or articles from thin layers of feed material. Additive manufacturing may involve applying liquid, layer, or particle material to a workstage, then sintering, curing, melting, and/or cutting to create a layer. The process is repeated up to several thousand times to construct the desired field finished component or article.
Often times it is necessary to pre-treat raw powder used in some of the additive manufacturing processes. Pre-treatment may include coating, degassing and heat treating the powder. The powder particles can be coated in order to prevent oxidation of the particles during the additive manufacturing process. For example, U.S. Pat. No. 7,141,207 discloses applying a copper coating to aluminum powder.
Degassing can be used to remove water vapor from the powder particles. Surfaces of the powder can become oxidized very quickly during the manufacturing process when exposed to the environment. Water vapor can absorb into the oxide, which can cause voids in the material formed with the additive manufacturing process. Methods of removing water from the manufactured materials can cause the forming of hydrogen which can make the final material more brittle. Previous methods of removing water vapor from the powder include various methods of degassing. For example, U.S. Pat. No. 5,976,456 describes a degassing method using heating aluminum powder in a vacuum to very high temperatures. However, complications can occur with maintaining a very low pressure vacuum during the degassing.
Additionally, traditional methods of high temperature heat treatment of gases can cause unwanted sintering of the powder. For example, fluidized beds have been used in conjunction with heat treating of powder to prevent agglomeration, as discussed in U.S. Pat. No. 6,811,765.
In particular, cold spray additive manufacturing requires removal of moisture and hydroxides on the surface of aluminum alloys at elevated temperatures to avoid detrimental effects in the final article such as blistering.